Barn layout

You can lay out compost barns for different feeding practices including:

Drive-by feeding (see figure 1)

Covered feeding

Drive-through feeding with pens on both sides

Bunk feeding (inside or outside)

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A 4-foot (1.2 m) high wall borders the pack on three sides and separates it from the feed alley.

The two outside walls can be cast-in-place concrete walls on footings below normal frost depths or wood. You can have the posts support the roof embedded in the outside walls or have the posts mounted on top of the wall. Make sure the structural engineer or the builder understand all structural loads including:

Manure load

Lateral earth pressure

Machine load

Roof load

Wind load

Wind lift load

Snow load

Others

The wall separating the pack area and the feed alley can be cast-in-place concrete or moveable, wide-based concrete panels, called Jersey walls. A fence on top of this wall can prevent cows from walking over it.

Walkways, at least 10 to 12 feet wide, provide cows and equipment access to the pack area. At minimum there should be a walkway at each end of the wall separating the pack and the feed alley. Long barns will need more walkways.

Locate waterers along the feed alley. You can place waterers on either side of the feed manger or next to the concrete wall separating the pack and the feed alley. Avoid placing waterers in the bedded pack area to:

Reduce wetting of the pack.

Keep the waterers cleaner.

Avoid having to adjust waterer height as pack depth increases.

Compost barns should have 3-foot eave overhangs to help prevent roof runoff and rain from blowing in. Roof gutters will also help keep roof runoff out. Slope the ground around a compost barn to reduce snow and rain runoff from entering the barn.

Figure 1. (not to scale) shows a compost barn layout for 100 cows with the following.

Three walkways to access the pack

Drive-by feeding

A 6-foot overhang

Waterers are against the concrete wall separating the bedded pack from the feed alley. Cows can only access them from the feed alley.

Managing the packed bedding

Compost barn pens start with a 1- to 1.5-foot layer of loose, dry fine wood shavings or sawdust. Add fresh bedding when the pack gets moist enough to stick to the cows after they lie down on it. The bedded area should provide 100 feet per cow of resting space.

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Aerate the bedding to a depth of 8 to 10 inches twice daily during milking. A modified cultivator on a skid loader or small tractor works well.

Aeration brings in oxygen, which may help aerobic breakdown of the bedding. It also provides a fresh surface with less manure for cows to lie down on after returning from milking or feeding. Some Minnesota producers aerate the pack deeper (about 16 to 18 inches) with a chisel-plow type of equipment. As a result, these producers didn’t need as much bedding and had increased

Typically, producers need to add a semi-truck load of fresh dry sawdust (approximately 18 tons) every two to five weeks. This amount will change based on the following.

Season

Weather

The number of cows

Some dairies may add smaller amounts of sawdust more often, such as once weekly. A small number of other dairies add a thin layer of bedding every day.

Usually, producers only remove bedding material from the pack area in the fall and spring. You only need to entirely clean out the pack area yearly in September or October.

After removing soiled bedding, producers usually add a load of clean sawdust. This sawdust provides a bedding layer 1 to 1.5 feet high to start the new pack. Most producers leave about 0.5 feet of old material in the barn to help start microbial activity.

By the end of summer, most packs average 4 feet high. Farms may remove some of the pack material in the spring to provide space for added bedding during the summer.

Producers spread soiled bedding on the fields according to their manure management plan. Others may pile soiled bedding to produce finished compost.

Ventilation

Compost dairy barns need good ventilation (air exchange) to:

Remove cow moisture and heat.

Remove pack moisture and heat from microbial activity.

Remove moisture and extend the time between bedding additions in the winter.

High moisture commonly appears as steam rising from the pack during aerating in cold weather. This moisture needs to leave the barn with the ventilation air.

Compost barns should have 16-foot sidewalls for better ventilation. This height also provides access for bedding trucks. The higher sidewall height in a compost barn, compared to a freestall barn, accommodates the sidewall opening lost from the pack walls.

Many compost barns have mixing fans to blow air down onto the pack, which helps dry the surface. Hang the fans high enough to provide head room for aerating equipment at the top pack-height.

Fertilizer value and pack temperatures

In a cross-sectional study we took samples of the pack at two depths. We analyzed these bedding samples for the following.

Moisture

Ammonia

pH

Total Carbon (C)

Nitrogen (N)

Phosphorus (P)

Potassium (K)

Electrical conductance (soluble salts) concentrations

Table 1 shows the results, which includes a column with recommended values for composting.

The average carbon to nitrogen (C:N) ratio was 19.5:1. A C:N ratio below 25:1 may give off ammonia odor, which may influence the ammonia levels in compost barns.

The average bedding temperature was 108 F. The pack surface temperatures were similar to the surrounding temperature. Temperatures were greater where the pack was fluffier, not as heavily soiled or packed by the cows. This observation was the same with the need for air to promote composting.

Costs

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Barn building costs have ranged from $50,000 to $300,000, with a cost per cow ranging from $625 to $1,750 (barn only, doesn’t include milking parlor). The building costs range widely depending on the amount of on-farm labor used and barn amenities added.

Bedding costs range from $0.45 to $1.00 per cow daily, depending on the source of sawdust and travel distance from the dairy.

Bedding costs and availability of bedding materials are a main concern producers have about compost barns. Sawdust is the best option for compost barns, but combining sawdust with the following can work relatively well.